Understanding telomere dynamics during embryogenesis has direct relevance to human disease. Recent studies in animal cloning found that the reconstructed embryos were able to restore the shortened telomeres in the donor cells to the normal range specific of that species, in cattle, pigs and mice, indicating that mechanisms exist for early embryonic cells to check and repair/restore telomere deficiency. The cloned embryos, therefore, provide a good model system to study the factors and pathways that regulate telomere homeostasis in early stage embryos. The objective of this R03 project is to establish an accurate telomere length assay for preimplantation stage embryos and to determine the telomere restoration dynamics in cloned bovine embryos. The specific aims are: 1) to establish a reliable PCR based telomere length assay Single Telomere Length Assay (STELA) for preimplantation stage embryos; and 2) to determine the telomere restoration dynamics of Xp chromosomes in cloned bovine embryos. The central hypothesis we want to test is that the telomeres are restored in cloned embryos in a stochastic and chromosome specific pattern. Knowledge obtained from this system will not only answer the intriguing question of when and how the telomeres are restored in cloned embryos, but also shed light on the more fundamental question of how telomere lengths are regulated in embryo development. [unreadable] [unreadable] [unreadable]